This portion of a phase diagram shows the vapor-pressure...

This portion of a phase diagram shows the vapor-pressure curves of a volatile solvent and of a solution of that solvent containing a nonvolatile solute. (a) Which line represents the solution? (b) What are the normal boiling points of the solvent and the solution? [Section 13.5$]$

Key Concepts

Boiling Point and Normal Boiling Point

The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure, leading to rapid vaporization. The normal boiling point is defined as the boiling point at standard atmospheric pressure (1 atm). In a phase diagram, the boiling point corresponds to the temperature where the vapor-pressure curve intersects the line representing the ambient pressure.

Phase Diagrams

Phase diagrams are graphical representations of the states of matter (e.g., solid, liquid, and gas) for a substance at various temperatures and pressures. They show the conditions under which these phases coexist and the transitions between them, providing a framework to understand phenomena such as boiling, freezing, and sublimation.

Vapor Pressure and Vapor-Pressure Curves

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature. Vapor-pressure curves on phase diagrams illustrate how the vapor pressure changes with temperature. For a solution, the addition of a nonvolatile solute reduces the vapor pressure compared to that of the pure solvent, shifting the curve downward.

Colligative Properties

Colligative properties are characteristics of solutions that depend on the number of solute particles relative to the solvent, rather than the specific type of particles. Key colligative effects include vapor-pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. These properties explain why adding a nonvolatile solute to a solvent alters its vapor pressure and boiling point.

Transcript

00:01 Welcome back.

00:01 We're working on chapter 13 problem 10, and we're looking at the following diagram that shows the vapor pressure curves of both a volatile solvent and a solution of a solvent containing a non -violetal solute.

00:15 And the information they want us to pull out is which line represents the solution, and what are the normal boiling points of a solvent and a solution? so let's break this down.

00:26 We know we have a solvent, and we know we have a solution.

00:30 So let's think about that.

00:32 Where have we heard about solvents and solutions before? so what's the difference between a pure solvent and a solution? a solution will be made of this solvent plus.

00:56 It'll have additional atoms in there.

01:00 And those additional atoms are going to increase our intermolecular forces.

01:14 So our intermolecular forces have been turned up.

01:17 So what's that going to do to our boiling point? if we have more intermolecular forces, that means we're going to have a higher boiling point.

01:27 So we've changed the boiling point just by adding additional molecules to there.

01:34 And that sounds like something we've heard of before.

01:36 Whenever we add salt to water, when we're boiling pasta, we're trying to increase the boiling point so that the pasta cooks faster.

01:44 So this is something we've done in the kitchen before.

01:46 So let's look at what we have on the graph here.

01:50 Let's look at the boiling points that we have...

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